This question comes up at least once a week on investing forums that I visit:
"Money markets are yielding nothing, so why not invest in a bond fund?"
Cash is not the same as a bond fund. If you need the safety of cash, then DODIX is not going to do that for you. You might select a short-term treasury bond fund as the next step up in risk, but you wouldn't select DODIX. If you didn't want the safety of cash, then why were you not already invested in the bond fund in the first place?
Another thread to read on this: Bogleheads :: View topic - On this quest for money market alternatives